5 Hours Ago
Tanking kits were certainly available in 2009/2010 when I refurbished my en-suite shower room, and from what I recall, these kits and other water repelling boards like Wedi and Hardie were available quite readily if you knew where to find them and what you were looking for, and had been around for some time.
My best suggestion would be to contact Mapei who do a paint-on type tanking kit, as well as a wallpaper type roll kit, and perhaps Wedi and James Hardie and ask them exactly when their tanking products hit the shelves in the UK.
But it does all come down to knowing that these products were around back then, and that your installer knew what they were and the merits of having them.
I had a paint-on kit for my shower room because the house-builder had done a particularly poor job at installing the shower area and frequently I ended up with puddles of water in the lounge below. Once bitten, twice shy.